It is known that porphyry copper deposits predominate over other metals in a mixed metal deposit, which contain, among others, iron oxide copper gold deposits (“IOCG) and volcanogenic massive sulfide deposits. Examples of porphyry copper deposits are those found in El Salvador, Chile, and Bingham, Utah. The copper mines of Arizona, USA, including the mines of Bisbee, Tiger, Tombstone, Morenci, Mammoth and Ajo, Ariz., are the result of the supergene enrichment and hydrothermal alteration of a porphyry copper sulfide intrusion.
Porphyry type copper ore deposits amenable to strip mining usually consist of a primary zone of essentially sulfides of copper containing minute quantities of gold, an overlying layer or secondary zone of essentially oxidized copper minerals also containing minute quantities of gold, and a transition zone in between.
Copper sulfides in the supergene enrichment zone at the groundwater interface are, in general, identified as the economically significant class of minerals. Copper oxides at near surface or surface deposits are often considered to be not all that profitable themselves, and important only to the extent that they point prospectors to the supergene enrichment zone below.
It has been estimated that approximately 85% of the world's copper mining supply comes in the form of sulfide mineral ores. The remaining 15% comes in the form of oxide mineral ores.
These porphyry copper deposits contain other valuable metals and minerals, such as gold and silver. The Bingham Canyon Mine, for example, as of 2004, has yielded more than 17 MM tons of copper, 23 MM oz gold, 190 MM oz silver and 850 MM lbs molybdenum. The gold and silver are impurities removed from copper during refining.
Unlike the primary zone that responds readily to conventional flotation procedures, the recovery of metal values from the secondary zone (the copper oxide zone or zone containing copper by-products) has been limited to the prevailing practice of acid heap leaching to extract the acid soluble component of copper. In this process, the mined ore is crushed into small chunks and heaped on an impermeable plastic and/or clay lined leach pad where it can be irrigated with a leach solution, such as sulfuric acid, to dissolve the valuable metals. Either sprinklers or often drip irrigation are used to minimize evaporation. The solution then percolates through the heap and leaches out the acid soluble copper minerals. This can take several weeks. The leach solution containing the dissolved metals is then collected. This leaves behind a gold-containing residue that is laden with acid.
The drawback with this practice is that the gold values in the secondary (essentially copper oxide) ore are virtually untouched, and because of their very low gold content are uneconomic to recover by other means, and thus, end up in the waste dump. Aside from this disadvantage, said process employs acid consumption—with a tremendous environmental impact requiring some form of remediation—and is costly. Add to this the long holding and processing time to recover the copper as well as the required area for the leaching pad.
Prior art shows processes that have been developed for the flotation of copper oxide ores such as sulphidization with xanthate collector flotation. However, these processes have drawbacks. For example, in sulphidization, there is difficulty in controlling the sulphidizing agent and the irritating odor of said agent. Likewise the use of sulfides depresses gold values and prevents them from being floated, hence, recovery would be difficult and costly.
A number of collectors have been evaluated for copper oxide flotation without sulphidization and these include organic complexing agents, fatty acids, fatty amines and petroleum sulphonates. However, these collectors have met with limited success in the field because of their lack of selectivity. Other reagents/collectors have been evaluated but these significantly affect the cost of the flotation processes for oxides.
Conventional collectors such as xanthates do not perform well on oxidized surfaces. Sulphydric collectors such as xanthates are the most common collectors, however, they are highly selective for sulfide minerals and they chemically react with the sulfide surfaces and do not have affinity for the common non-sulfide minerals such as oxide or oxidized copper sulfide minerals. Studies have been made to combine xanthates with other collectors.
For example, U.S. Pat. No. 4,022,686 provides a flotation process for copper sulfide and copper oxide ores and for copper smelter slags, wherein benzotriazole or alkyl benzotriazole is added to the ground ores as an activator and then add one or more collectors selected from the group consisting of xanthates, dithiophosphates, thiocarbamate esters, dithiocarbamates, mercaptans and dixanthogens and further, if desired, a promoter such as kerosene, light oil, bunker oil or petroleum lubricant is added to improve the recovery for the flotation of copper ores or copper smelter slags. The conditioning of oxide ores by the addition of benzotriazole or alkylbenzotriazole is claimed to have a higher copper recovery than the sulfidizing process. The process however, is known to be viable for high grade ores.
GB 2029274A and GB 20096262 also describe other processes for the recovery of metal concentrates from mineral ores containing a metal or metal in the form of their sulphides and/or oxides by froth flotation of the crushed ore and using as collector a 2-mercapto aromatic amine and ortho hydroxyl phenyl oxime respectively. Both processes may have limited application to mineral ores containing one or more metals, i.e. copper, zinc, platinum, molybdenum, nickel, lead, antimony arsenic, silver and gold.
For gold recovery, the most common process is cyanide leaching, using cyanide to dissolve the gold. Froth flotation is usually applied when the gold present in an ore is closely associated with sulfide minerals. Direct cyanidation of gold-bearing ore generates tons of waste materials containing cyanide which can constitute an environmental hazard.
U.S. Pat. No. 4,710,361 describes the process of sulfhydric-fatty acid flotation at a pH range of about 5 to 8, in the recovery of gold from gold ores/cyanidation tailings. Likewise, WO2009/072908 provides another process for gold recovery by separating the sand from the primary slime, separating further the sand from the secondary slime and treating sand fractions with sulfhydric-fatty acid collector at a pH of about 6 to 8. These processes however apply only to gold recovery.
The above mentioned disadvantages or problems in the prior arts are solved by the present invention.